Using archaeomagnetism to unravel the occupational history of a medieval site: Cañada Real (Burgos, Northern Spain)

Abstract

Different attempts to date the archaeological site of Cañada Real (Northern Spain) with radiocarbon yielded contrasting results, ranging from the Bronze Age to medieval times. During the archaeological interventions carried out there, a well-preserved burned surface was discovered. The burned sediments of this surface offered the opportunity to conduct full-vector archaeomagnetic dating to elucidate the age of the studied site. For determination of an archaeomagnetic intensity, two different methods (Thellier-Coe and Tsunakawa-Shaw) were applied to test their suitability and compare their reproducibility. Raman spectroscopy and rock magnetism revealed that the main magnetization carrier is magnetite, with varying concentrations of hematite and goethite. A good correlation is observed between high Qn ratio values (typically > 6) and strongly magnetic as well as stable orthogonal demagnetization diagrams of the natural remanent magnetization. The full-vector was recovered with a mean direction of Declination = 17.7°, Inclination = 54.0°, α95 = 3.2°, k = 309.2 and a mean intensity of 38.1 ± 9.0 µT. Comparison to the SCHA.DIF.4 k geomagnetic field model yielded a single dating interval of 995–1125 CE at 95 % confidence level. This result accurately dates one of the phases of abandonment of the site and coincides with some historically documented Muslim razzias, demonstrating the usefulness of the archaeomagnetic technique to reconstruct the occupational history of archaeological sites with burned remains.